Hydrogels

ABSTRACT

A method of producing a hydrogel product comprises impregnating a coherent fibrous structure with an aqueous solution of a hydrogel precursor material said fibers incorporating cations which are capable of cross-linking said precursor material to form a fiber reinforced hydrogel as the hydrogel product.

[0001] The present invention relates to hydrogels, i.e. cross-linkedmacromolecular networks which are swollen with water or biologicalfluids. The invention relates more particularly, but not exclusively, tosuch hydrogels that are useful as wound dressings.

[0002] A hydrogel is a cross-linked macromolecular network swollen withwater or biological fluids. It is known that hydrogels are useful aswound dressings, particularly because of their ability to donate fluidto a wound to maintain a moist “healing environment”. There are howeverdisadvantages with prior art hydrogel dressings (e.g. Clearsite) in thatthey can be weak and difficult to handle.

[0003] It is therefore an object of the present invention to obviate ormitigate the above disadvantages.

[0004] According to a first aspect of the present invention there isprovided a method of producing a hydrogel product comprisingimpregnating a coherent fibrous structure (preferably sterilised) withan aqueous solution of a hydrogel precursor material (preferablysterilised), said fibers incorporating cations which are capable ofcross-linking said precursor material to form a fiber reinforcedhydrogel as the hydrogel product.

[0005] By “coherent fibrous structure” we mean that the fibrousstructure is comprised of fibres which are positively held together tomaintain the overall coherency of the structure although obviously we donot preclude the possibility that individual fibres of the structure maybecome loose and detached. Such structures are to be distinguished from,for example, loose chopped fibres in which there is no mechanical forcesholding the fibres together into the form of a structure. Examples ofcoherent fibrous structures which may be used in accordance with theinvention are knitted, woven, and non-woven products such as felts,matts and the like. A preferred fibrous structure is a non-woven felt.

[0006] A particularly preferred fibrous structure is a non-woven feltmade of calcium alginate fibres and having a basis weight of 30 to 200gsm, more preferably 40 to 80 gsm, and most preferably about 60 gsm.

[0007] The method of the invention is effected by impregnating thefibrous structure with the solution of hydrogel precursor, preferably inratio (by weight) of solution:fabric of (20-70):1. The method results inthe production of a hydrogel which has been cross-linked (i.e. “set”) byions released from the fibres. In the final hydrogel the fibrousstructure provides, in effect, a reinforcement giving strength for easyhandling of the hydrogel. If desired the hydrogel product may beautoclaved.

[0008] Hydrogels produced in accordance with the invention may be in theform of sheets typically having a thickness of 1 mm to 10 mm.

[0009] The hydrogels are in a hydrated form and are capable of donatingmoisture to a wound. The hydrogels may be used for treating superficialwounds with low to medium levels of exudates

[0010] Examples of hydrogel precursor material which may be used includesodium alginate, sodium carboxymethyl cellulose, sodium pectinate,sodium O-carboxymethyl chitosan (OCC), sodium N,O-carboxymethyl chitosan(NOCC), sodium polyacrylate, and naturally occurring gums and syntheticpolymers containing pendant carboxylic acid groups (hummectants).

[0011] The hydrogel precursor may consist wholly or partially of AceMannan (or other component of Alloe Vera) which is a natural polymerknown to accelerate healing of wounds. The Ace Mannan may, for example,provide up to 80% of the matrix. The Ace Mannan may be clinical gradematerial obtainable from Carrington Laboratories, Dallas, Tex., U.S.A.

[0012] The hydrogel precursor may, if desired, incorporate an agent tostimulate the healing of wounds. Examples of such agents include growthfactors, e.g. whey growth factor extract (obtainable from GroPep Ltd.Australia) or Prezatide copper acetate complex (obtainable from Procyte,U.S.A.),

[0013] The fibres which are used contain a di- or higher valent cationwhich is effective for cross-linking the hydrogel. Examples of suitablecations include Ca²⁺, Zn²⁺, and cations which also act as enzymecofactors. Particular preferred examples of fibres which may be used arecalcium alginate fibres.

[0014] Preferably the hydrogel precursor solution incorporates abacteriostatic agent, preferably propylene glycol.

[0015] In a preferred method of carrying out the invention, the hydrogelprecursor (e.g. an alginate) is dissolved in a mixture of 75%-85% byweight water and 15% to 25% by weight propylene glycol. The resultantsolution is then used to impregnate the coherent fibrous structure toform the hydrogel.

[0016] It is possible for the hydrogel precursor solution and coherentfibrous structure to be supplied separately whereby the method of thefirst aspect of the invention may be effected in, for example, asurgery. This affords the possibility of either using the coherentfibrous structure as a dressing per se or using it to produce a hydrogelproduct as discussed above.

[0017] Therefore according to a second aspect of the invention there isprovided a kit of parts for producing a hydrogel product the kitcomprising a container of a hydrogel precursor solution (preferablysterilised) and a coherent fibrous structure (preferably sterilised).

[0018] Hydrogel products obtained in accordance with the invention maybe used in conjunction with hydrophilic films which have an increasedbreathability in the presence of liquid water as compared to moisturevapour alone. The use of such a film over the hydrogel (i.e. on the sideremote from the wound) ensures that water is vented from the hydrogelthrough the film. Therefore the dissolution of the hydrogel may becontrolled,

[0019] Typically the breathable film will be of a material which, as a50 micron film, has an MVTR in the presence of moisture vapour alone of6,000 to 10,000 g m⁻² 24 hr⁻¹ as measured by ASTM E96B and an MVTR inthe presence of a liquid water (as measured by ASTM E96BW) of 6,000 to10,000 g m⁻² 24 hr⁻¹. Typically the breathable film will lave athickness of 30-70 microns, more preferably 40-60 microns, e.g. about 50microns.

[0020] The breathable film may for example be of polyurethane. Suitablefilms are available from Innovative Technologies Limited under thedesignations IT325, IT425 and IT625.

[0021] The invention is illustrated with reference to the followingnon-limiting Example.

EXAMPLE

[0022] A none-woven felt made of calcium alginate MF1-2A felt, availablefrom Innovative Technologies) having a weight/unit area of about 60 g/m²was treated with a 2% alginate (Protanol LF 10/60, ex-Pronava) dissolvedin a 80/20 mixture of water and propylene glycol. The ratio of solutionto felt was 40 to 1. The solution was first spread out in a flatstainless steel dish having a size of about 30 cm×30 cm and the felt wasthen placed in solution. The fibres interacted with the sodium alginatein the solution to form a sheet hydrogel. The resultant gel could beautoclaved to provide a hydrated sheet hydrogel for treating superficialwounds with low to medium level of exudate.

1. A method of producing a hydrogel product comprising impregnating acoherent fibrous structure with an aqueous solution of a hydrogelprecursor material capable of being cross-linked to form a hydrogel,said fibres incorporating cations which are capable of cross-linkingsaid precursor material to form a fibre reinforced hydrogel as thehydrogel product.
 2. A method as claimed in claim 1 wherein the coherentfibre structure is a knitted, woven or non-woven product.
 3. A method asclaimed in claim 2 wherein the coherent fibre structure is a felt ormatt.
 4. A method as claimed in any one of claims 1 to 3 wherein thehydrogel precursor is sodium alginate, sodium carboxymethyl cellulose,sodium pectinate, sodium O-carboxymethyl chitosan (OCC), sodiumN,O-carboxymethyl chitosan (NOCC), sodium polyacrylate, and naturallyoccurring gums and synthetic polymers containing pendant carboxylic acidgroups (hummectants).
 5. A method as claimed in any one of claims 1 to 3wherein the hydrogel precursor consists wholly or partially of AceMannan (or other component of Alloe Vera).
 6. A method as claimed in anyone of claims 1 to 5 wherein the hydrogel precursor incorporates anagent to stimulate the healing of wounds.
 7. A method as claimed in anyone of claims 1 to 6 wherein said cations are Ca²⁺, Zn²⁺ and/or cationswhich also act as enzyme cofactors.
 8. A method as claimed in any one ofthe preceding claims wherein the fibres are calcium alginate fibres. 9.A method as claimed in any one of the preceding claims wherein thehydrogel precursor is dissolved in a mixture of 75% to 85% by weightwater and 15% to 25% by weight propylene glycol.
 10. A method as claimedin any one of the preceding claims wherein the ratio by volume of thehydrogel precursor solution to the coherent fibre structure is (20 to70):1.
 11. A hydrogel product which comprises a hydrogel and areinforcement of a fibrous structure which is coherent per se.
 12. Ahydrogel product as produced by the method of any one of claims 1 to 10or as claimed in claim 11 for use as a primary wound dressing forsuperficial wounds with low to medium levels of exudate.
 13. A kit ofparts for producing a hydrogel product, the kit comprising a containerof a hydrogel precursor solution (preferably sterilised) and a coherentfibrous structure (preferably sterilised).